Abstract:In this work, several tests of thermal cycling under constant load are carried out on Ti-45.0Ni-5.0Cu (at%) shape memory wires. The properties related to the Stress Assisted Two Way Memory Effect (SATWME) of the material are investigated as a function of the mechanical loading history for the same temperature range during cooling and heating. For this reason, two thermomechanical tests have been employed: tests I, where one sample is used for just one constant stress level test and tests II, where only one sam… Show more
“…As indicated in figure 9(d), for stresses as high as 100 MPa, a relative stability of SME was observed, but accompanied by an important accumulation of plastic strain under load. These behaviors are similar to those in Cu-25.9Zn-4.0Al (wt%) ribbons by Benchiheub et al [21] and in Ti-Ni based thin wires [6,22].…”
Nowadays, some compositions of Cu-Zn-Al alloys are commercially available with the potential to present shape memory properties after a suitable thermomechanical treatment. Applied as sensor and/or actuator, the smallest product of Cu-based shape memory alloys (SMA) are wires 0.5 mm in diameter. This paper focuses on Cu-25.3Zn-4.0Al (wt%) wires, 0.5 mm in diameter, that were supplied by Societé Tréfimetaux (France) in a cold drawn condition, without any martensitic transformation. After betatization heat treatment of the SMA wires, physical characterization was carried out through an optical micrograph, DSC and x-ray diffraction while the thermomechanical behavior of the samples was verified by thermal cycling under a constant load. The results obtained have demonstrated the appearance of a two-step transformation which causes an important change in the strain-temperature behavior. This phenomenon is rarely observed in these Cu-Zn-Al SMA.
“…As indicated in figure 9(d), for stresses as high as 100 MPa, a relative stability of SME was observed, but accompanied by an important accumulation of plastic strain under load. These behaviors are similar to those in Cu-25.9Zn-4.0Al (wt%) ribbons by Benchiheub et al [21] and in Ti-Ni based thin wires [6,22].…”
Nowadays, some compositions of Cu-Zn-Al alloys are commercially available with the potential to present shape memory properties after a suitable thermomechanical treatment. Applied as sensor and/or actuator, the smallest product of Cu-based shape memory alloys (SMA) are wires 0.5 mm in diameter. This paper focuses on Cu-25.3Zn-4.0Al (wt%) wires, 0.5 mm in diameter, that were supplied by Societé Tréfimetaux (France) in a cold drawn condition, without any martensitic transformation. After betatization heat treatment of the SMA wires, physical characterization was carried out through an optical micrograph, DSC and x-ray diffraction while the thermomechanical behavior of the samples was verified by thermal cycling under a constant load. The results obtained have demonstrated the appearance of a two-step transformation which causes an important change in the strain-temperature behavior. This phenomenon is rarely observed in these Cu-Zn-Al SMA.
“…Electrical resistivity measurements coupled with thermomechanical tests in Ti-Ni polycrystalline alloys have confirmed a linear variation of ER as a function of strain 11,12 . The ER was also used to study the Two Way Shape Memory Effect (TWSME) phenomenon as a function of stress, strain and number of cycles during training process 9,[12][13][14] .…”
Section: Introductionmentioning
confidence: 79%
“…The ER was also used to study the Two Way Shape Memory Effect (TWSME) phenomenon as a function of stress, strain and number of cycles during training process 9,[12][13][14] .…”
Recently, electrical resistivity (ER) measurements have been done during some thermomechanical tests in copper based shape memory alloys (SMA's). In this work, single crystals of Cu-based SMA's have been studied at different temperatures to analyse the relationship between stress (σ) and ER changes as a function of the strain (ε). A good consistency between ER change values is observed in different experiments: thermal martensitic transformation, stress induced martensitic transformation and stress induced reorientation of martensite variants. During stress induced martensitic transformation (superelastic behaviour) and stress induced reorientation of martensite variants, a linear relationship is obtained between ER and strain as well as the absence of hys teresis. In conclusion, the present results show a direct evidence of martensite electrical resistivity anisotropy.
“…The evaluation of the mechanical behavior and the shape memory effect of the actuator was performed by repeating 40 times the heating and cooling cycle for each applied load (stress) of 35, 70, 105, 135, 170 and 200 MPa 15,16 . Figure 2 shows the main parameters from a generic thermo-elastic deformation curve.…”
Section: Experimental Partmentioning
confidence: 99%
“…During the training process, M s temperature decreases with number of cycles for small stress value, while for stress above 135 MPa the evolution is the inverse. In the first case, the M s temperature decreases because of dislocation reorientation which modifies the internal stress and points the martensitic variant in the preferential direction 16,24 . In the second case, the M s temperature increases for high stress due to fast martensitic reconfiguration and exhaustion (practically all martensitic variants were immediately activated by stress) 23 .…”
Section: Training Process Of the Actuatorsmentioning
The development of shape memory actuators has enabled noteworthy applications in the mechanical engineering, robotics, aerospace, and oil industries and in medicine. These applications have been targeted on miniaturization and taking full advantage of spaces. This article analyses a Ti-Ni shape memory actuator used as part of a flow control system. A Ti-Ni spring actuator is subjected to thermomechanical training and parameters such as transformation temperature, thermal hysteresis and shape memory effect performance were investigated. These parameters were important for understanding the behavior of the actuator related to martensitic phase transformation during the heating and cooling cycles which it undergoes when in service. The multiple regression methodology was used as a computational tool for analysing data in order to simulate and predict the results for stress and cycles where the experimental data was not developed. The results obtained using the training cycles enable actuators to be characterized and the numerical simulation to be validated.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.